docs: def sdiff(a, b):
      """
      Take the symmetric difference of two sets of any data type to form a
      third set.
  
      http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/sdiff_c.html
  
      :param a: First input set.
      :type a: spiceypy.utils.support_types.SpiceCell
      :param b: Second input set.
      :type b: spiceypy.utils.support_types.SpiceCell
      :return: Symmetric difference of a and b.
      :rtype: spiceypy.utils.support_types.SpiceCell
      """
      assert isinstance(a, stypes.SpiceCell)
      assert isinstance(b, stypes.SpiceCell)
      assert a.dtype == b.dtype
      # The next line was redundant with the [raise NotImplementedError] line below
      # assert a.dtype == 0 or a.dtype == 1 or a.dtype == 2
      if a.dtype is 0:
          c = stypes.SPICECHAR_CELL(a.size, a.length)
      elif a.dtype is 1:
          c = stypes.SPICEDOUBLE_CELL(a.size)
      elif a.dtype is 2:
          c = stypes.SPICEINT_CELL(a.size)
      else:
          raise NotImplementedError
      libspice.sdiff_c(ctypes.byref(a), ctypes.byref(b), ctypes.byref(c))
      return c